Curated Optogenetic Publication Database

Abstract: Genetically encoded biosensors based on the principle of Förster resonance energy transfer comprise two major classes: biosensors based on fluorescence resonance energy transfer (FRET) and those based on bioluminescence energy transfer (BRET). The FRET biosensors visualize signaling-molecule activity in cells or tissues with high resolution. Meanwhile, due to the low background signal, the BRET biosensors are primarily used in drug screening. Here, we report a protocol to transform intramolecular FRET biosensors to BRET-FRET hybrid biosensors called hyBRET biosensors. The hyBRET biosensors retain all properties of the prototype FRET biosensors and also work as BRET biosensors with dynamic ranges comparable to the prototype FRET biosensors. The hyBRET biosensors are compatible with optogenetics, luminescence microplate reader assays, and non-invasive whole-body imaging of xenograft and transgenic mice. This simple protocol will expand the use of FRET biosensors and enable visualization of the multiscale dynamics of cell signaling in live animals.

Abstract: The extracellular signal-regulated kinase (ERK) plays a central role in the signaling cascades of cell growth. Here, we show that stochastic ERK activity pulses regulate cell proliferation rates in a cell density-dependent manner. A fluorescence resonance energy transfer (FRET) biosensor revealed that stochastic ERK activity pulses fired spontaneously or propagated from adjacent cells. Frequency, but not amplitude, of ERK activity pulses exhibited a bell-shaped response to the cell density and correlated with cell proliferation rates. Consistently, synthetic ERK activity pulses generated by a light-switchable CRaf protein accelerated cell proliferation. A mathematical model clarified that 80% and 20% of ERK activity pulses are generated by the noise and cell-to-cell propagation, respectively. Finally, RNA sequencing analysis of cells subjected to the synthetic ERK activity pulses suggested the involvement of serum responsive factor (SRF) transcription factors in the gene expression driven by the ERK activity pulses.